Although lack of empathy has been considered a central characteristic of Asperger syndrome, quantitative and qualitative assessments of empathy in this syndrome are lacking. We present two cases of adolescents with Asperger syndrome who show extreme deficits on measures of both cognitive and affective empathy. Analysis of their performance on tasks assessing cognitive and affective processing did not reveal significant impairment in executive functions, nor in their ability to recognize emotions or the ability to create a mental representation of another person's knowledge. However, both patients were unable to integrate the emotional content with mental representations and deduce the other person's emotional state. These results suggest that impaired empathy in individuals with Asperger syndrome may be due to impaired integration of the cognitive and affective facets of the other person's mental state.